Process for burning hydrocarbons and cracked products in exhaust gases from sintering machines

ABSTRACT

Hydrocarbons and cracked products present in exhaust gases from a sintering process are withdrawn in a sintering zone and are burned by being passed through hot sintered material in a cooling zone subsequent to the sintering operation. The process is especially suited for burning hydrocarbons and cracked products in exhaust gases from an iron oxide-containing sintering operation.

United States Patent [1 1 Cappel et al.

[451 Dec. 31, 1974 PROCESS FOR BURNING HYDROCARBONS AND CRACKED PRODUCTS IN EXHAUST GASES FROM SINTERING MACHINES [75] lnventors: Fred Cappel, Sprendlingen; Jurgen Otto, Nieder-Eschbach; Siegfried Nikl, Frankfurt am Main; Hans Rausch, Oberursel, all of Germany 73 Assignee: Metallgesellschaft Aktiengesellschaft,

Frankfurt am Main, Germany [22] Filed: Nov. 14, 1972 [21] Appl. No.: 306,491

[30] Foreign Application Priority Data Nov. 17, 1971 Germany 2l57044 [52] US. Cl. 75/5, 75/3 [51] Int. Cl C2lb 1/18 [58] Field of Search 75/3, 5

[56] References Cited UNITED STATES PATENTS 3 ,264,09 1

8/1966 Ban ..7s/4x 3,311,465 3/ 1967 Ban 'et al 75/5 3,649,244 3/1972 Cunningham 75/5 FOREIGN PATENTS OR APPLICATIONS 498,837 l/ 1939 Great Britain 75/5 1,118,030 6/1968 Great Britain 75/5 Primary ExaminerWinston A. Douglas Assistant Examiner-Thomas A. Waltz Attorney, Agent, or Firm-Burgess, Dinklage & Sprung [5 7] ABSTRACT 4 Claims, 4 Drawing Figures j id PATENTEI] DEBS] I974 SHEET 2 OF 2 PROCESS FOR BURNING IIYDROCARBONS AND CRACKED PRODUCTS IN EXHAUST GASES FROM SINTERING MACHINES BACKGROIJND This invention relates to a process for burning hydrocarbons and/or cracked products derived from organic constituents of iron oxide-containing sinterable mixtures in the exhaust gases from sintering machines.

Sintering machines on which iron ores and materials which contain iron oxideare sintered by being ignited and passed through by oxygen-containing gases produce exchaust gases which contain hydrocarbons and cracked products derived from organic constituents of the mixture being sintered. These substances may enter the sintering process, for example, with the fuels used in the process, with flotation agents or with recycled substances. The exhausts are not removed by the gaspurifying means following the sintering operation or partly condense in the electrostatic dust collector which can give rise to troubles such as fire. Such exhaust gases always contain such substances and pollute the-air.

SUMMARY DESCRIPTION OF THE DRAWINGS FIGS. 1 through 4 are diagrammatic views in side elevation illustrating several embodiments of the process of the invention.

DESCRIPTION The exhaust gases are preferably conducted through a cooling zone which is provided on the sintering machine and begins at the point where the ignition zone in the sinterable mixture just reaches the grateprotecting layer.

The cooling may be performed using suction or pressure.

The entire exhaust gas may be passed through the cooling zone if the mixed temperature of all exhaust gases from the sintering machine is below about 80C.

In a preferred embodiment of the invention, the exhaust gases which contain hydrocarbons and/or cracked products are withdrawn from-those wind boxes which when viewed in the direction of travel in the sintering machine precede a point which closely follows the point where the expulsion of the hydrocarbons and- /or cracked products has been terminated. In this case, a cooler exhaust gas which contains hydrocarbons and- /or cracked products is formed at a lower volumetric rate. The point where the expulsion is terminated is generally close to the point where the water has been expelled from the sinterable mixture and the temperature of the exhaust gases rises more rapidly.

In a preferred feature, the exhaust gases which contain hydrocarbons and/or cracked products are withdrawn from the wind boxes disposed under that portion ofthe sintering machine in which a major portion ofthe hydrocarbons and/or cracked products are expelled. As a result, the volumetric rate of the exhaust gas to be supplied to the cooling zone may be reduced and an effective removal of the hydrocarbons and/or cracked products may nevertheless be obtained.

In a further preferred feature, the exhaust gases withdrawn from the wind boxes which contain hydrocarbons and/or crackedproducts are introduced into the portion of the cooling zone forward of the sintering zone. In the following portion of the cooling zone, cold air may be passed through the sintered mixture. This practice results in a good combustion of the hydrocarbons and cracked products and also in a good cooling along a short path.

According to another feature, exhaust gases from the wind boxes disposed under that portion of the sintering machine which receives the sinterable mixture when the expulsion of water therefrom has been terminated are recycled into the ignition box. Because hot exhaust gases are used in theignition box, less fuel is required for the ignition so that hydrocarbons and cracked products are produced at a lower rate.

The invention will be more fully understood from the following description of the embodiments shown in the drawings and the examples wherein reference is made to the several figures of the drawing.

Referring now to the drawing and in particular to FIGS. 1 through 4 show several embodiments of sintering machines 1 having an upper course which moves in the direction of the arrow 2. The sintering mixture is ignited in the ignition box 3. Wind boxes 4, 4a, 4b, 4c, 4d are disposed under that portion of the sintering machine in which sintering is effected. The wind boxes are diagrammatically indicated as respective individual wind boxes but may consist of a plurality of individual wind boxes, which are connected to a gas-collecting manifold. The gas-collecting manifolds for the wind boxes are designated 5, 5a, 5b, 5c, 5d. The sintering air is sucked by blowers (not shown) through the sinterable mixture into the wind boxes. Wind boxes 6a and 6b are disposed under that portion of the sintering machine which is operated as a cooler. A gas-collecting hood is disposed over the forward portion of the cooling zone. Through conduit 8, the gases are conducted from the hood 7 to the dust collector, not shown. Cool ing air is forced into the rear portion of the cooling zone through conduit 9.

The following examples relate to a sintering machine having a sintering area of I00 square meters and a cooling area of square meters. The core mixture which is processed has the following composition:

Ores 63% including hydrocarbons Roll scale 8% including 0.8% hydrocarbons Blast furnace flue dust 6% including 0.1% hydrocarbons Blast furnace flue dust mud 3% including 0.9% hydrocarbons Dolomite 8% including hydrocarbons Limestone l2% including hydrocarbons 100 parts of the mixture are sintered together with 50% returns, 7 parts fuel, and 6.5 parts water. Sinter is produced at a rate of 146 metric tons per hour, as well as exhaust gas at a rate of 272,400 standard cubic meters per hour. The exhaust gas contains 20% of the hydrocarbons which had been fed in. (Herinafter, the term hydrocarbons will cover both hydrocarbons and cracked products.)

EXAMPLE 1 (FIG. 1)

The exhaust gases from the entire sintering portion were withdrawn from wind boxes 4 through conduit and had a mixed temperature of about 80C. The exhaust gas rate is 272,400 standard cubic meters per hour. The exhaust gas contains 142 milligrams hydrocarbons per standard cubic meter. The entire exhaust gas is conducted into the wind boxes 4-and 6a which are disposed under the first 62% of the length of the cooling area. From the wind boxes 6a, the gas flows through the hot sintered material into the gascollecting hood 7 and is withdrawn through conduit 8. Cooling air is forced through conduit 9 into wind boxes 6b, which are disposed under the remaining 38% of the length of the cooling area.

EXAMPLE 2 (FIG. 2)

The mixed temperature of all exhaust gases from the sintering portion is about 160C.

Wind boxes 4d are disposed under the first 75% of the length of the sintering area. Wind boxes 40 are disposed under the remaining 25%. Viewed in the direction of travel of the sintering machine 1, the wind boxes 4d may terminate closely behind that point at which the expulsion of the hydrocarbons has been terminated. Exhaust gases at a rate of 190,000 standard cubic meters per hour are withdrawn from the wind boxes 4d through conduit 5d and introduced into the wind boxes 6a. These exhaust gases contain 203 milligrams hydrocarbons per standard cubic meter. The wind boxes 6a are disposed under the first 43% of the length of the cooling area. Cooling air is forced through conduit 9 into the wind boxes 61;, which are disposed under the remaining 57% of the length of the cooling area.

Through conduit 50, exhaust gases at a rate of 82,400 standard cubic meters per hour and at a temperature of about 300C, are withdrawn from the wind boxes4c, which are disposed under the remaining 25% of the length of the sintering area. These exhaust gases are virtually free of hydrocarbons and are conducted to the dust collector.

EXAMPLE 3 (FIG. 3)

The mixed temperature of all exhaust gases from the sintering portion is about 160C.

The wind boxes 4b are disposed under the intermediate 50% of the length of the sintering area, the wind boxes 4a under the first 25% and the wind boxes 4c under the last 25%. Exhaust gases at a rate of 126,500 standard cubic-meters per hour and at a temperature of 60C. are withdrawn from the wind boxes 4b through conduit 5b and fed into the wind boxes 6a. These exhaust gases contain 274 standard cubic meters per hour. This includes about 90% of the hydrocarbon content of all exhaust gases.

The wind boxes 6a are disposed under the first 29% of the length of the cooling area. Cooling air is forced through conduit 9 into the wind boxes 6b disposed under the remaining 71% of the length of the cooling area.-

Exhaust gases at a rate of 63,500.standard cubic me- EXAMPLE 4 (FIG. 4

The process conditions are the same as in Example 2 but the exhaust gases withdrawn from wind boxes 4c in conduit Sc are fed into the ignition box 3 so that less fuel is added and the exhaust gases withdrawn from the wind boxes 4d contain only 195 milligrams hydrocarbons per standard cubic meter.

In all examples, the exhaust gas withdrawn in conduit 8 from the gas-collecting hood 7 contains virtually no hydrocarbons or only a few milligrams thereof.

The advantages of the invention reside in that the exhaust gases discharged from the sintering plant contain much less or virtually no hydrocarbons or cracked products and these impurities are removed in an economical manner.

What is claimed is:

1. Process for burning hydrocarbons and/or cracked products present in exhaust gases from the sintering of iron' oxide mixtures on a sintering machine having a sintering zone followed by a cooling zone which consists essentially of:

i. withdrawing exhaust gases having a temperature below about C containing substantially all of the hydrocarbons and/or cracked products from the mixturebeing sintered via wind boxes positioned under a portion of the sintering zone which includes the point in said sintering zone where hydrocarbons and/or cracked products cease to be expelled from the mixture being sintered; and

ii. thereafter passing the exhaust gases withdrawn in step (i) directly through the hot sintered material in a first portion of the cooling zone which follows the sintering, the hydrocarbons and/or cracked products in said exhaust gas being burned in the hot sintered material.

2. Process of claim 1 wherein the exhaust gases are withdrawn in step (i) by two successive groups of wind boxes, about 10 percent of the amount of the hydrocarbons and/or cracked products expelled from the mixture being sintered being withdrawn via the first group of wind boxes and the balance of about percent being withdrawn via the second group of wind boxes, the exhaust gases withdrawn via the second group of wind boxes being passed through the hot sintered material and burned as in 'step (ii).

3. Process of claim l wherein exhaust gases virtually free of hydrocarbons and/or cracked products are withdrawn from the mixture being sintered via wind boxes positioned under a second portion of the sintering zone which follows the point where hydrocarbons and/or cracked products cease to be expelled from the mixture being sintered.

4. Process of claim 3 wherein the exhaust gases free of hydrocarbons and/or cracked products are recycled to the ignition box of the sintering machine. 

1. PROCESS FOR BURINGING HYDROCARBONS AND/OR CRACKED PRODUCTS PRESENT IN EXHAUST GASES FROM THE SINTERING OF IRON OXIDE MIXTURES ON A SINTERING MACHINE HAVING A SINTERING ZONE FOLLOWED BY A COOLING ZONE WHICH CONSISTS ESSENTIALLY OF: I. WITHDRAWING EXHAUST GASES HAVING A TEMPERATURE BELOW ABOUT 80*C CONTAINING SUBSTANTIALLY ALL OF THE HYDROCARBONDS AND/OR CRACKED PRODUCTS FROM THE MIXTURE BEING SINTERED VIA WIND BOXES POSITIONED UNDER A POSITION OF THE SINTERING ZONE WHICH INCLUDES THE POINT SAID SINTERING ZONE WHERE HYDROCARBONS AND/OR CRACKED PRODUCTS CEASE TO BE EXPELLED FROM THE MIXTURE BEING SINTERED; AND II. THEREAFTER PASSING THE EXHAUST GASES WITHDRAWN IN STEP (I) DIRECTLY THROUGH THE HOT SINTERED MATERIAL IN A FIRST PORTION OF THE COOLING ZONE WHICH FOLLOWS THE SINTERING, THE HYDROCARBONS AND/OR CRACKED PRODUCTS IN SAID EXHAUST GAS BEING BURNED IN THE HOT SINTERED MATERIAL.
 2. Process of claim 1 wherein the exhaust gases are withdrawn in step (i) by two successive groups of wind boxes, about 10 percent of the amount of the hydrocarbons and/or cracked products expelled from the mixture being sintered being withdrawn via the first group of wind boxes and the balance of about 90 percent being withdrawn via the second group of wind boxes, the exhaust gases withdrawn via the second group of wind boxes being passed through the hot sintered material and burned as in step (ii).
 3. Process of claim 1 wherein exhaust gases virtually free of hydrocarbons and/or cracked products are withdrawn from the mixture being sintered via wind boxes positioned under a second portion of the sintering zone which follows the point where hydrocarbons and/or cracked products cease to be expelled from the mixture being sintered.
 4. Process of claim 3 wherein the exhaust gases free of hydrocarbons and/or cracked products are recycled to the ignition box of the sintering machine. 